FIG. 1 is a circuit diagram showing an embodiment of the conventional alternating current generator for a car. In the figure, the reference nuemral 1 designates an armature coil having a three phase connection for generating an alternating current output and the numeral 2 designates a field coil, these parts constituting a three phase alternating current generator. The reference numeral 3 designates a main rectifying device for rectifying the alternating current output of the armature coil 1; the numeral 4 designates an auxiliary rectifying device for rectifying the alternating current output of the armature coil 1; the numeral 5 designates a voltage controlling device which turns on and off an exciting current passing to the field coil 2; the numeral 6 designates a key-switch; the numeral 7 designates a charge lamp connected to the key-switch 6 in series; and the numeral 8 designates a battery.
The positive side of the battery 8 charged by the output of the main rectifying device 3 is connected to the voltage controlling device 5 through a serial connection of the key-switch 6, a charge lamp 7 and the field coil 2. The output of the auxiliary rectifying device 4 is, on one hand, connected to the voltage controlling device 5 and is, on the other hand, connected to the voltage controlling device 5 through the field coil 2.
The operation of the circuit constructed as above-mentioned will be described.
First of all, when the key-switch 6 is closed, an exciting current is passed to the field coil 2 through a circuit of the positive (+) side of battery 8--key-switch 6--charge lamp 7--field coil 2--voltage controlling device 5--negative (-) side of battery 8. After this, when an engine is actuated for revolution whereby the terminal voltage of the generator increases, an exciting current is supplied from the auxiliary rectifying device 4 to the field coil 2 and the generator starts to generate power as a self-excited generator.
In such alternating current generator constructed as above-mentioned, however, a part of an output current is consumed as an exciting current to cause reduction in output from the exciting current corresponding to about ten percent of the output current of the generator and to cause consumption of excessive power of the engine disadvantageously.